This invention relates to detergent compositions and, in particular, to detergent compositions which have controlled sudsing characteristics, especially those useful in automatic dishwashing.
Detergent compositions normally contain surfactants which tend to produce foam when agitated in aqueous solution. For many applications, especially in automatic washing and dishwashing machines, excess foam production is a serious problem with detergent compositions and with many effective surfactants it is necessary to add foam inhibiting compounds, hereinafter called suds suppressors, in order to achieve acceptable sudsing characteristics.
Unfortunately, it has been found that the addition of suds suppressors can in itself create new problems. For example, monostearyl acid phosphate, which is one conventional suds suppressor, is very effective and useful at low levels in the product, but as the level of suds suppressor is increased to cope, for example, with increased surfactant, then the suds suppressor becomes incompletely soluble in a wash solution and precipitates out of solution onto utensil and machine surfaces leaving them coated with unsightly streaks and deposits.
Another type of suds suppressor which has often been suggested is that based on silicones, especially polydimethylsiloxane. These materials, referred to generically hereinafter as silicone suds suppressors, are known to be very useful in industrial applications where the silicone suds suppressor is added directly to an aqueous solution containing a surfactant. However, they have not lived up to their promise when incorporated into detergent compositions; frequently, for example, they become inactivated in the presence of other detergent ingredients and require some type of special protection.
It has now been found that stable suds suppressed detergent compositions can be prepared by incorporating silicone materials into the compositions in a particular manner.
Accordingly, it is an object of the invention to provide detergent compositions which are storage-stable and which include silicone suds suppressors.
It is a further object of the invention to provide a process for the incorporation of silicone suds suppressors into detergent compositions to provide storage-stable suds-suppressed compositions.
Another problem exhibited by conventional silicone suds suppressors, such as polydimethylsiloxane, is that they are either completely inactivated in the spray-drying process or they lose their activity very quickly after the spray-dried granules have been made.
In the preparation of spray-dried detergent granules an aqueous mixture of the various components of the granules (the crutcher mix) is sprayed or otherwise introduced into what is essentially a drying tower. As the droplets of the crutcher mix proceed through the drying tower, the water is flashed off and solid or semiporous detergent granules are secured. The advantage of spray-dried detergent granules over granules obtained by simple dry mixing of the individual ingredients is their homogeneity. That is to say, each granule contains the various ingredients in the same ratio proportions introduced into the original crutcher mix. This provides obvious advantages over simple dry mix detergent formulations, inasmuch as dry mixing can result in a lack of homogeneity in the final detergent formulations such that the user is never certain of the composition of any given portion of the product.
In order to provide a homogeneous spray-dried granule it is necessary that the crutcher mix, itself, be substantially homogeneous. In some instances, a crutcher mix may be a homogeneous solution. However, in order to provide a crutcher solution, excess amounts of water are needed to dissolve all the components. Use of excessive amounts of water requires additional drying capacity in the spray-dry tower and is not economically attractive. For the most part, the crutcher mixes employed in the preparation of spray-dried detergent compositions are semidissolved aqueous slurries of the various components desired in the final spray-dried granules.
The crutching and spray-drying process, while possessing the above advantages, does create a problem with regard to the incorporation into the granules of relatively sensitive ingredients, such as the conventional silicone suds suppressors, at least partly as a result of the high alkalinity and temperatures present during the crutching stage. Such ingredients can of course be incorporated into the composition after spray-drying, for example, by dry mixing or spraying on. But the necessity of such an extra step in the process is undesirable. In addition, certain ingredients, especially those present in minor amounts, are not easy to distribute uniformly throughout a spray-dried granular composition. Clearly then, a very desirable way to include a silicone suds suppressor into a detergent composition would be simply to add the material directly to the crutcher mix before spray-drying.
Furthermore, it is known that the introduction of alkoxylated nonionic surfactants into an aqueous detergent crutcher mix tends to cause inhomogeneity in the mix. This is because the nonionic materials tend to be oily and to exist in a separate phase. This problem can be helped by the use of agents such as certain alkyl phosphate esters or preferably, as is taught in the copending U.S. patent application Ser. No. 589,116, by R. M. Wise, filed June 23, 1975, by using kaolinite or bentonite clays. However, this problem of inhomogeneity in the crutcher mix is exacerbated by the addition of conventional silicone suds suppressors, such as polydimethysiloxane, since these materials are themselves oily and do not disperse well either in water or in nonionic surfactant.
It is therefore an additonal object of this invention to provide spray-dried detergent granules which include a nonionic surfactant and also a silicone suds suppressor.
It is a further object herein to provide an improved process for the incorporation of certain silicone suds suppressors into spray-dried detergent granules containing substantial quantities of nonionic surfactant.